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| Format: | Preprint |
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2026
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| Online Access: | https://arxiv.org/abs/2602.02322 |
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| author | Marques-Chaves, R. Álvarez-Márquez, J. Colina, L. Kendrew, S. Abdurro'uf Blanco-Prieto, C. Boogaard, L. A. Castellano, M. Caputi, K. I. Crespo-Gomez, A. Fontana, A. Fudamoto, Y. Fujimoto, S. García-Marín, M. Harikane, Y. Harish, S. Hashimoto, T. Hsiao, T. Iani, E. Inoue, A. K. Langeroodi, D. Lin, R. Melinder, J. Napolitano, L. Ostlin, G. Pérez-González, P. G. Prieto-Jiménez, C. Rinaldi, P. Del Pino, B. Rodríguez Santini, P. Sugahara, Y. Varo-O'ferral, A. Wright, G. Zavala, J. |
| author_facet | Marques-Chaves, R. Álvarez-Márquez, J. Colina, L. Kendrew, S. Abdurro'uf Blanco-Prieto, C. Boogaard, L. A. Castellano, M. Caputi, K. I. Crespo-Gomez, A. Fontana, A. Fudamoto, Y. Fujimoto, S. García-Marín, M. Harikane, Y. Harish, S. Hashimoto, T. Hsiao, T. Iani, E. Inoue, A. K. Langeroodi, D. Lin, R. Melinder, J. Napolitano, L. Ostlin, G. Pérez-González, P. G. Prieto-Jiménez, C. Rinaldi, P. Del Pino, B. Rodríguez Santini, P. Sugahara, Y. Varo-O'ferral, A. Wright, G. Zavala, J. |
| contents | We present very deep (~11h) JWST/MIRI low-resolution spectroscopy of the rest-frame optical emission of U37126, a UV-bright (M_UV ~ -20), mildly lensed ($μ\simeq 2.2$) galaxy at z=10.255. The continuum emission is well detected in both NIRSpec and MIRI spectra, yet no nebular recombination or metal emission lines are observed (EW(Hbeta+[OIII])<300A and EW(Halpha)<400A, at 3sigma). Combined with the exceptionally blue UV continuum slope, beta_UV ~ -2.9, and weak/flat Balmer break, these constraints indicate a stellar population dominated by very young and massive stars with a strongly suppressed nebular contribution. Comparisons with synthetic stellar population models indicate that U37126 requires both a very high ionizing photon production efficiency, log(Xi_ion / Hz erg^-1) ~ 25.75, and a nearly unit LyC escape fraction, of fesc>86% (3sigma) based on Halpha flux limit and fesc=0.94+/-0.06 derived independently from SED fitting. The best-fit SED yields a (de-lensed) stellar mass of Mstar ~ 10^7.8 Msun and a star-formation rate of SFR~10Msun/yr (sSFR~160 Gyr^-1), that along with its very compact size, reff~61pc, yields very high stellar mass and star-formation-rate surface densities, Sigma_M ~ 3x10^3 Msun/pc^2 and Sigma_SFR ~ 400 Msun/yr/kpc^2. Together with the lack of detectable nebular emission, these properties suggest that U37126 is undergoing an ``ISM-naked'' starburst phase, possibly driven by an extremely efficient gas-to-star conversion followed by strong feedback that has cleared the remaining gas from its stellar core, allowing most LyC photons to escape. Finally, we show that even a small fraction of galaxies like U37126 (~ 3%-6%), with extreme LyC production and escape, could contribute disproportionately (~ 50%-100%) to the ionizing photon budget during cosmic reionization. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2602_02322 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | PRISMS. U37126, a very blue, ISM-naked starburst at z=10.255 with nearly 100% Lyman continuum escape fraction Marques-Chaves, R. Álvarez-Márquez, J. Colina, L. Kendrew, S. Abdurro'uf Blanco-Prieto, C. Boogaard, L. A. Castellano, M. Caputi, K. I. Crespo-Gomez, A. Fontana, A. Fudamoto, Y. Fujimoto, S. García-Marín, M. Harikane, Y. Harish, S. Hashimoto, T. Hsiao, T. Iani, E. Inoue, A. K. Langeroodi, D. Lin, R. Melinder, J. Napolitano, L. Ostlin, G. Pérez-González, P. G. Prieto-Jiménez, C. Rinaldi, P. Del Pino, B. Rodríguez Santini, P. Sugahara, Y. Varo-O'ferral, A. Wright, G. Zavala, J. Astrophysics of Galaxies We present very deep (~11h) JWST/MIRI low-resolution spectroscopy of the rest-frame optical emission of U37126, a UV-bright (M_UV ~ -20), mildly lensed ($μ\simeq 2.2$) galaxy at z=10.255. The continuum emission is well detected in both NIRSpec and MIRI spectra, yet no nebular recombination or metal emission lines are observed (EW(Hbeta+[OIII])<300A and EW(Halpha)<400A, at 3sigma). Combined with the exceptionally blue UV continuum slope, beta_UV ~ -2.9, and weak/flat Balmer break, these constraints indicate a stellar population dominated by very young and massive stars with a strongly suppressed nebular contribution. Comparisons with synthetic stellar population models indicate that U37126 requires both a very high ionizing photon production efficiency, log(Xi_ion / Hz erg^-1) ~ 25.75, and a nearly unit LyC escape fraction, of fesc>86% (3sigma) based on Halpha flux limit and fesc=0.94+/-0.06 derived independently from SED fitting. The best-fit SED yields a (de-lensed) stellar mass of Mstar ~ 10^7.8 Msun and a star-formation rate of SFR~10Msun/yr (sSFR~160 Gyr^-1), that along with its very compact size, reff~61pc, yields very high stellar mass and star-formation-rate surface densities, Sigma_M ~ 3x10^3 Msun/pc^2 and Sigma_SFR ~ 400 Msun/yr/kpc^2. Together with the lack of detectable nebular emission, these properties suggest that U37126 is undergoing an ``ISM-naked'' starburst phase, possibly driven by an extremely efficient gas-to-star conversion followed by strong feedback that has cleared the remaining gas from its stellar core, allowing most LyC photons to escape. Finally, we show that even a small fraction of galaxies like U37126 (~ 3%-6%), with extreme LyC production and escape, could contribute disproportionately (~ 50%-100%) to the ionizing photon budget during cosmic reionization. |
| title | PRISMS. U37126, a very blue, ISM-naked starburst at z=10.255 with nearly 100% Lyman continuum escape fraction |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2602.02322 |